1. Field of the Invention
The present invention relates to a charged-particle beam writing method, and more specifically to a pattern writing method with a charged-particle beam in which the charged-particle beam is deflected using a main deflector and a sub deflector both disposed on the optical path of the charged-particle beam and a predetermined pattern is written onto a sample located on a stage.
2. Background Art
FIG. 11 is the schematic configuration of an electron beam writing system disclosed in Japanese patent laid-open No. 284392/1998 (Hei 10-284392). In the figure, a stage 103 with a sample 102 such as a mask mounted thereon is accommodated inside a sample chamber 101. The stage 103 is driven by a stage driving circuit 104 in the direction of X (direction horizontal to this sheet) and in the direction of Y (obverse-reverse direction of the sheet). The moved position of the stage 103 is measured by a position or location circuit 105 using a laser length measurement unit or the like.
An electron beam optical system 1010 is disposed above the sample chamber 101. The electron beam optical system 1010 is made up of an electron gun 106, various lenses 107, 108, 109, 1011 and 1012, a blanking deflector 1013, a beam size varying deflector 1014, a main deflector 1015 for beam scanning, a sub deflector 1016 for beam scanning, and two beam shaping apertures 1017 and 1018, etc.
A position to be irradiated with an electron beam is positioned in a predetermined subfield by the main deflector 1015. A pattern writing position is located within the subfield by the sub deflector 1016. The beam size varying deflector 1014 and the beam shaping apertures 1017 and 1018 control the shape of the electron beam. Pattern writing processing in the subfield is conducted by moving the stage 103 continuously in one direction. At this time, the processing proceeds to exposure of the next subfield after the completion of exposure of one subfield.
After the end of drawing of a frame corresponding to a set of a plurality of subfields, the stage 103 is moved in steps in the direction perpendicular to the direction of its continuous movement. By repeating the above processing, respective frame areas are written sequentially. Here, the frame is a strip-like pattern writing area determined depending on the deflection width of the main deflector 1015. On the other hand, the subfield is a unitary pattern writing area determined depending on the deflection width of the sub deflector 1016.
A magnetic disk 1021 corresponding to a storage medium is connected to a control computer 1020. Pattern writing data for a mask is stored in the magnetic disk 1021. The pattern writing data read from the magnetic disk 1021 is temporarily stored for each frame area in a pattern memory 1022. The pattern data for each frame area stored in the pattern memory 1022, or frame information comprising a pattern writing position, pattern writing graphic data, etc. is analyzed by a pattern data decoder 1023 and a pattern writing data decoder 1024 each corresponding to a data analysis section.
The output of the pattern data decoder 1023 is sent to a blanking circuit 1025 and a beam shaping driver 1026. That is, the pattern data decoder 1023 creates blanking data, based on the above data and sends the same to the blanking circuit 1025. Further, desired beam size data is also created and sent to the beam shaping driver 1026. A predetermined deflection signal is applied from the beam shaping driver 1026 to the beam size varying deflector 1014 of the electron optical system 1010, whereby the size of the electron beam is controlled.
The output of the pattern writing data decoder 1024 is sent to a main deflection sensitivity correcting unit 1031. The main deflection sensitivity correcting unit 1031 performs a sensitivity correction to a main deflector driver 1027 according to a main deflection position (subfield pattern writing position) in the frame and sends the corrected data to the main deflector driver 1027 and a sub deflection sensitivity correcting unit 1032. The sub deflection sensitivity correcting unit 1032 transfers the optimum sub deflection sensitivity for the main deflection position corrected by the main deflection sensitivity correcting unit 1031 to a sub deflector driver 1028. Here, the corrected data of the main deflection sensitivity correcting unit 1031 and the sub deflection sensitivity correcting unit 1032 are determined upon deflection/calibration of an electron beam prior to actual pattern writing and stored in their corresponding memories attached thereto in advance by the control computer 1020. Incidentally, the corrected data of the sub deflection sensitivity correcting unit 1032 is created by detecting a sensitivity shift in sub deflection produced depending on the main deflection position in advance.
A predetermined deflection signal is applied from the main deflector driver 1027 to the main deflector 1015 of the electron optical system 1010 to deflect and scan the electron beam in a designated main deflection position. The sub deflection sensitivity correcting unit 1032 generates a control signal for sub deflector scanning and sends it to the sub deflector driver 1028. Then, a predetermined sub deflection signal is applied from the sub deflector driver 1028 to the sub deflector 1016, whereby pattern writing inside each subfield is performed.
In such an electron beam writing system, bending due to own weight of the mask occurs in the mask with the mask mounted on the stage. In doing so, each pattern formed onto the mask is distorted so that a desired pattern cannot be formed. With the foregoing in view, Japanese patent laid-open No. 250394/1996 (Hei 8-250394) has disclosed that a signal obtained by applying an electron beam to a mask is detected to obtain positional information about each pattern formed on the mask, the height of the surface of the mask is measured to determine or obtain bending of the mask, and the positional information about the pattern is corrected based on the so-obtained bending.
In the Japanese patent laid-open No. 250394/1996 (Hei 8-250394), the amounts of position corrections in the directions of X and Y caused by the bend of the mask are calculated by determining coefficients of a function descriptive of a surface shape by the method of least squares. Described specifically, assuming that data obtained by measuring the height at a plurality of different positions are used and the height measured relative to a position (x, y) on the mask is z, the surface shape is represented by coefficients a0 through a14 of a function constituted of the following equation:
          ⁢      z    =                  a        0            +                        a          1                ⁢        x            +                        a          2                ⁢        y            +                        a          3                ⁢                  x          2                    +                        a          4                ⁢        xy            +                        a          5                ⁢                  y          2                    +                        a          6                ⁢                  x          3                    +                        a          7                ⁢                  x          2                ⁢        y            +                        a          8                ⁢                  xy          2                    +                        a          9                ⁢                  y          3                    +                        a          10                ⁢                  x          4                    +                        a          11                ⁢                  x          3                ⁢        y            +                        a          12                ⁢                  x          2                ⁢                  y          2                    +                        a          13                ⁢                  xy          3                    +                        a          14                ⁢                  y          4                    
However, the method of calculating a correction value at an arbitrary point (x, y) of a pattern writing area by the electron beam on the basis of one function is unfit where the correction amount increases locally at part of the pattern writing area.
Therefore, Japanese patent laid-open No. 256122/1998 (Hei 10-256122) has described that a pattern writing area is divided into plural areas and the correction of pattern writing positions in the areas are performed independently of each other.